WHITEFISH OF THE LAKE OF GENEVA 



with them and then grows progressively wider. The 

 little crustaceans feed upon these first creatures; they, 

 in their turn, serve as prey to the larger fishes, of which 

 the divers species, according to their size and nature, 

 live upon one another, hunting down and devouring 

 one another. Then these last, so far as the lake itself 

 is concerned, complete the series. The remains of the 

 strongest, when at last they die, decompose, break up 

 into their elements and go back to the mineral world. 

 And the cycle goes on continually, always begun, 

 always unfinished, bringing it to pass that all the 

 inhabitants of the lake are more closely associated in 



Fig. 35. — Bythotrephes longimanus, planktonic crustacean of the order 

 Cladocera. The length, without the terminal appendage, is between 

 2 and 3 millimetres. 



their search for subsistence. Beneath the peaceful 

 sparkling waters of the lake, the depths are ceaselessly 

 occupied by hosts of pursuers and pursued, in this 

 continual chase after food, in this uninterrupted con- 

 sumption of the flesh of one to build up the flesh of 

 another. 



We too are not indifferent to this state of affairs. 

 When, at dawn, the fisherman pulls up his net, full 

 of fish which he will send to the market — hoping to 

 make a living out of the proceeds — he takes his share 

 of the profits to be drawn from the whole cycle. For 

 him, for us, the unicellular creatures, the tiny crus- 

 taceans, expend their vital energies, from which we 

 can draw no advantage directly. The water which 

 fills the lake: the sunshine which irradiates its surface 

 182 



